1. Field of the Invention
The present invention relates to an optical member and a method of manufacturing the same. More specifically, the present invention relates to an optical member having an oxide layer forming a fine textured structure on the surface of the member and a method of manufacturing the same.
2. Description of the Related Art
For example, eyeglass lenses, optical lenses, solar panels, cathode-ray tubes, filters, and display panels are required to produce a small amount of light scattering and have low reflection surfaces. This requirement is achieved by using a single- or multi-layer antireflection coating whose refractive index and thickness is controlled to have certain values. However, the antireflection properties of the coating change, depending on the wavelength and the angle of incidence, and the realization of high-performance antireflection properties in broad ranges of the wavelengths and the angles of incidence is difficult.
In addition, it is known that a fine texture formed on the surface of glass can impart an antireflection function to the glass. In particular, an antireflection function over a broad range of the angle of incidence can be expected if the texture is smaller than the wavelength. As methods for producing such a fine texture, chemical etching or mechanical processing of glass surfaces is proposed. But, it is difficult, using chemical etching and the mechanical processing, to achieve a fine texture having structures separated by a distance that is smaller than the wavelength of visible light. Thus, chemical etching or mechanical processing that can realize antireflection properties for an application requiring transparency in the wavelength range of visible light has not been developed. Furthermore, a coating film forming a textured structure on a glass surface has been investigated. For example, Japanese Patent Publication No. 61-48124 discloses an antireflection coating formed on a transparent material, such as glass, by converting a metal film of aluminum, magnesium, zinc, or an alloy thereof into an oxide or a hydroxide and this antireflection coating constitutes discrete leeflets having various heights and shapes. Japanese Patent Laid-Open No. 9-202649 discloses a transparent alumina film that is randomly agglomerated like a petal. The film is formed by applying a coating solution containing at least an aluminum alkoxide and a stabilizer onto a substrate to form an amorphous alumina film, treating the film hydrothermally, and drying it.
Many coating films as shown in Japanese Patent Publication No. 9-202649 are generally porous. In general, glasses having a high refractive index used as base materials contain oxide components such as an alkali oxide, an alkaline earth oxide, or boric oxide that are low in resistance to water and humidity. If these glasses are used as a base material for coating, water or humidity in the air penetrates the surface of the base material, and an alkali oxide, an alkaline earth oxide, or boric oxide contained in the base material is released to cause fogging or whitening of the surface or the interface thereof. In addition, in the case of porous oxides, especially their unstable components such as a water-soluble component and a component that is dissolved and re-deposited in water undergo a hydration reaction when the base material having a surface layer of porous oxides is brought into contact with moisture. As a result, the glasses' optical characteristics deteriorate with time. Furthermore, dissolution or corrosion of such a composition caused by the porous oxide itself may occur under an atmosphere containing an acid.